1. Field of the Invention
The present invention relates to a liquid cooling apparatus, and more particularly, to an ultrasonic atomizing cooling apparatus.
2. Description of the Related Art
As rapid growth of electronic, telecommunications and optoelectronics industries continue, related products tend to provide more versatile functions. As such, the integrity of transistors on chips, which govern various functions and performances of products, is increased. A heat dissipation problem accompanied reduced reliability of devices and systems. For example, with respect to optical-communication parts, excess heat causes chip to become damaged, and may also change the output optical wavelength. An investigation conducted by the United States Army shows the ratio of failure for electronic systems caused by temperature is as high as 55%, and the power consumption tends to increase following Moore's law.
Currently, many industries and research groups are dedicated to developing various cooling techniques to overcome the high power consumption problems of devices, such as the active cooling method and passive cooling method, including the thermoelectric, thermosyphon two-phase flow, single phase in microchannel, two phases in microchannel and the cryogenic cooling method. The liquid cooling method is regarded as a potential power dissipation method that may be able to replace the air-cooling method for the next generation. Recent developments of liquid cooling in chips are focused on direct contact with the chips, such as jet impingement cooling and spray cooling, wherein atomized droplets formed by the assembly manufactured by the microelectromechanical systems (MEMS) process are sprayed onto the chips. The heat is taken away through a phase change of the atomized droplets absorbing thermal energy dissipated from the chip. The jet impingement cooling and the spray cooling are regarded as potential liquid cooling methods for the future. However, the process for manufacturing these assemblies by the micromachining method is very complicated and troublesome. The manufacturing cost is a bottleneck to commercialize the two liquid cooling methods. Moreover, high pressure is required to spray the atomized droplets onto the chips in a uniform liquid film, and to avoid the accumulation of droplets on the chip due to liquid cohesion.
U.S. Pat. No. 6,247,525 B1 discloses a vibration-induced atomizer 30, which integrates an ultrasonic vibration device and a heat-exchange chamber. FIG. 1 is a cross-sectional view of the vibration-induced atomizer 30, which integrates with a chamber 31 filled with a liquid 38 in a gaseous phase. The wall 32 of chamber 31 makes contact with a heat-producing body 33 and the wall 34 of chamber 31 makes contact with a cooling device 36 provided with a plurality of piezoelectric disks 39A-39D. The piezoelectric disks 39A-39D are attached to the exterior surface 35 of the cooling wall 34 and a plurality of condensation sites 46 are formed on the portion of the inner surface 40 of the cooling surface 34 relative to the piezoelectric disks 39B-39C. The piezoelectric disks 39A-39D connect with a driver 42 via wires 41. When the temperature of the liquid 38 in gaseous phase rises, the liquid 38 in gaseous phase along the interior surface 40 of the wall 34 begins to condense and accumulate in the condensation sites 46. Aided by the vibration of the piezoelectric disks 39A-39D, the liquid accumulated in the condensation sites 46 transforms into atomized droplets 44 carrying energy. The atomized droplets 44 release from the wall 34, spraying onto the wall 32 and absorb heat of the wall 32 delivered from the heat-producing body 33. As such, the atomized droplets 44 are vaporized and the heat of the heat-producing body 33 is dissipated. However, the structure of the vibration-induced atomizer 30 confines the application itself. The vibration-induced atomizer 30 cannot fit various heat-producing bodies 33 with different positioning orientations, such as chips positioned with different orientations on printed circuit boards.
Accordingly, the intention is to provide an ultrasonic liquid cooling apparatus, which can fit various heat sources having different positioning orientations.